What is creatinine?
Creatinine is a waste product that comes from the normal wear and tear on muscles of the body. Everyone has creatinine in their bloodstream.

Can my healthcare provider know if my kidneys are working properly by looking at how much creatinine is in my blood?
No. Looking at how much creatinine is in your blood is not the best way to check your kidney health. That’s because the level of what is creatinine in your blood is affected by your age, race, gender, and body size. (In other words, what’s considered “normal” depends on these factors.) The best way to know if your kidneys are working properly is by looking at your glomerular filtration rate (GFR).
GFR is a routine lab that can be found on your blood work report.GFR is a calculation that includes your creatinine, along with your age, gender, race, and weight. Your GFR number will help your healthcare provider know if you have kidney disease.

Do I need any other tests?
Yes, another important test to check kidney function is a urine test. You will be asked to pee into a clean cup called a specimen cup. Only about two tablespoons of urine is needed to do the test. The urine will be sent to a laboratory, where a test called an ACR (albumin-to-creatinine ratio) is done. An ACR shows whether you have a type of protein called albumin in your urine. A normal amount of albumin in your urine is less than 30 mg/g. Anything above 30 mg/g may mean you have kidney disease, even if your GFR number is above 60.
This test is also used to look at how likely it is that a person’s kidney disease will get worse. This is called risk for progression. Having high amounts of albumin points to a higher risk.

Are there any instances when creatinine alone can be used to determine kidney function?
This is an important question. There is a difference between looking at what is creatinine in your bloodstream (called “serum creatinine”) and looking at creatinine in your urine (called “creatinine clearance”). These are two different lab tests.Serum creatinine is part of a routine lab report; creatinine clearance is not.
Creatinine clearance requires a timed urine sample. All the urine you have passed within a specific time period – usually 24-hours – is saved (collected) in a container and tested. The result shows how much creatinine has passed through your kidneys into your urine. It helps show how well your kidneys are removing the waste products from your blood.